Method and apparatus for providing downlink acknowledgements and transmit indicators in an orthogonal frequency division multiplexing communication system

ABSTRACT

A communication system provides downlink acknowledgments corresponding to uplink transmission using hybrid automatic repeat request to multiple users in an Orthogonal Frequency Division Multiplexing communication system, wherein a frequency bandwidth comprises multiple frequency sub-carriers, by spreading each acknowledgment of multiple acknowledgments with a selected spreading sequence of multiple spreading sequences to produce multiple spread acknowledgments, wherein each acknowledgment is intended for a different user of the multiple users, and distributing the multiple spread acknowledgments across the multiple frequency sub-carriers.

CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

The present application is a continuation of, and claims priority from,application Ser. No. 11/692,400, entitled “METHOD AND APPARATUS FORPROVIDING DOWNLINK ACKNOWLEDGMENTS AND TRANSMIT INDICATORS IN ANORTHOGONAL FREQUENCY DIVISION MULTIPLEXING COMMUNICATION SYSTEM,” filedMar. 28, 2007, and further claims priority from provisional applicationSer. No. 60/798,485, entitled “METHOD AND APPARATUS FOR PROVIDINGDOWNLINK ACKNOWLEDGMENTS AND TRANSMIT INDICATORS IN AN ORTHOGONALFREQUENCY DIVISION MULTIPLEXING COMMUNICATION SYSTEM,” filed May 8,2006, which applications are commonly owned and incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to Orthogonal Frequency DivisionMultiplexing (OFDM) communication systems and, in particular, toprovision of downlink acknowledgments and transmit indicators in an OFDMcommunication system.

BACKGROUND OF THE INVENTION

The IEEE (Institute of Electrical and Electronics Engineers) 802.16standards propose using an Orthogonal Frequency Division Multiple Access(OFDMA) for transmission of data over an air interface. OFDMA also hasbeen proposed for use in 3GPP (Third Generation Partnership Project)Evolution communication systems. In an OFDMA communication system, afrequency bandwidth is split into multiple contiguous frequencysub-carriers that are transmitted simultaneously. A user may then beassigned one or more of the frequency sub-carriers for an exchange ofuser information, thereby permitting multiple users to transmitsimultaneously on the different sub-carriers. These sub-carriers areorthogonal to each other, and thus intra-cell interference is minimized

In such systems, voice data is exchanged via Voice over InternetProtocol (VoIP). It is known to improve such systems for VoIP trafficusing hybrid automatic repeat request (HARQ) error correction schemesand smaller packet sizes. While VoIP users have the same benefits ofadvanced link adaptation and statistical multiplexing as data users, thegreatly increased number of users that may be served because of thesmaller voice packet sizes places a burden on control and feedbackmechanisms of the system. For example, it can be easily envisioned that30 times as many voice packets, and corresponding users, could be servedin a given frame than data packets. There are typically about 1600 bytesfor data and about 40-50 bytes for voice. However, present downlinkresource allocation and acknowledgment mechanisms typically allocate aresource block per user for conveyance of acknowledgments and thereforeare not designed to handle such a large number of allocations andconsume an inordinate amount of power and bandwidth in order toguarantee accurate detection and decoding at an edge of a cell.

Therefore, a need exists for a method and apparatus that provide fordownlink resource allocation and acknowledgments to multiple users andfurther guarantee accurate detection and decoding at an edge of a cellwithout consuming an inordinate amount of system power and bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communication system inaccordance with an embodiment of the present invention.

FIG. 2 is a block diagram of a user equipment in accordance with anembodiment of the present invention.

FIG. 3 is a block diagram of an exemplary uplink resource assignmentmessage in accordance with an embodiment of the present invention.

FIG. 4 is a block diagram of an exemplary uplink resource assignmentmessage in accordance with another embodiment of the present invention.

FIG. 5 is a table diagram illustrating an exemplary group schedulingsetup in accordance with an embodiment of the present invention.

FIG. 6 is a block diagram depicting an exemplary spreading of multipledownlink acknowledgments across an OFDMA frequency bandwidth inaccordance with an embodiment of the present invention.

FIG. 7 is a block diagram of an architecture of a Node B of FIG. 1 inaccordance with an embodiment of the present invention.

FIG. 8 is a logic flow diagram of a method executed by a Node B of FIG.1 in conveying downlink acknowledgments to one or more users equipmentof FIG. 1 in accordance with an embodiment of the present invention.

FIG. 9 is a block diagram of an OFDMA mapping function and an OFDMAmodulator of FIG. 7 in accordance with an embodiment of the presentinvention.

FIG. 10 is a block diagram of an OFDMA mapping function and an OFDMAmodulator of FIG. 7 in accordance with another embodiment of the presentinvention.

FIG. 11 is a block diagram of an exemplary OFDMA modulator of FIG. 7 inaccordance with an embodiment of the present invention.

FIG. 12 is a logic flow diagram illustrating a reception of anacknowledgment by a user equipment of FIG. 1 that has been scheduled fora downlink acknowledgment channel during a given time period inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

To address the need for a method and an apparatus that provide fordownlink resource allocation and acknowledgments to multiple users andfurther guarantee accurate detection and decoding at an edge of a cellwithout consuming an inordinate amount of system power and bandwidth, acommunication system is provided that provides downlink acknowledgmentscorresponding to uplink transmission using hybrid automatic repeatrequest to multiple users in an Orthogonal Frequency DivisionMultiplexing communication system, wherein a frequency bandwidthcomprises multiple frequency sub-carriers, by spreading eachacknowledgment of multiple acknowledgments with a selected spreadingsequence of multiple spreading sequences to produce multiple spreadacknowledgments, wherein each acknowledgment is intended for a differentuser of the multiple users, and distributing the multiple spreadacknowledgments across the multiple frequency sub-carriers.

Generally, an embodiment of the present invention encompasses a methodfor providing downlink acknowledgments corresponding to uplinktransmission using hybrid automatic repeat request to multiple users inan Orthogonal Frequency Division Multiplexing (OFDM) communicationsystem wherein a frequency bandwidth comprises multiple frequencysub-carriers. The method includes spreading each acknowledgment ofmultiple acknowledgments with a selected spreading sequence of multiplespreading sequences to produce multiple spread acknowledgments, whereineach acknowledgment is intended for a different user of the multipleusers, and distributing the multiple spread acknowledgments across themultiple frequency sub-carriers.

Another embodiment of the present invention encompasses a method forreceiving an acknowledgment corresponding to uplink hybrid automaticrepeat request transmission in an OFDM communication system wherein afrequency bandwidth comprises multiple frequency sub-carriers. Themethod includes monitoring a downlink control channel informing a userequipment (UE) of an uplink grant, determining the UE is scheduled totransmit data during a given time period based on the uplink grant, andtransmitting data during the time period. The method further includesreceiving an acknowledgment corresponding to the UE's uplinktransmission via multiple sub-carriers, wherein the acknowledgmentcomprises a spreading sequence associated with the UE and wherein thespreading sequence is distributed over the multiple sub-carriers in thefrequency bandwidth, and decoding the acknowledgment using a selectedacknowledgment sequence number.

Yet another embodiment of the present invention encompasses a method fora method for assigning a resource block in an OFDM communication system.The method includes assembling a resource assignment message havingmultiple transmit indicators, wherein a position of each transmitindicator in the message corresponds to a resource unit assigned to aUE, and conveying the resource assignment message using an uplink grantdata field on a downlink control message.

Still another embodiment of the present invention encompasses a wirelessnetwork element that provides downlink acknowledgments corresponding touplink transmission using hybrid automatic repeat request to multipleusers in an OFDM communication system wherein a frequency bandwidthcomprises multiple of frequency sub-carriers. The wireless networkelement includes a processor that is configured to use a first resourceunit number assigned to a UE in an uplink grant to select anacknowledgment spreading sequence number, spread each acknowledgment ofmultiple acknowledgments with a selected spreading sequence of multiplespreading sequences to produce multiple spread acknowledgments, whereineach acknowledgment is intended for a different user of the multipleusers, and distribute the multiple spread acknowledgments across themultiple frequency sub-carriers.

Yet another embodiment of the present invention encompasses a userequipment (UE) that receives an acknowledgment corresponding to uplinkhybrid automatic repeat request transmission in an OFDM communicationsystem wherein a frequency bandwidth comprises multiple frequencysub-carriers. The user equipment includes a processor that is configuredto monitor a downlink control channel informing the UE of an uplinkgrant, determine that the UE is scheduled to transmit data during agiven time period based on the uplink grant, transmit data during thetime period, receive an acknowledgment corresponding to the UE's uplinktransmission via multiple sub-carriers, wherein the acknowledgmentcomprises a spreading sequence associated with the UE and wherein thespreading sequence is distributed over the multiple sub-carriers in thefrequency bandwidth, and decode the acknowledgment using a selectedacknowledgment sequence number.

Still another embodiment of the present invention encompasses a wirelessnetwork element that assigns a resource block in an OFDM communicationsystem. The wireless network element includes a processor that isconfigured to assemble a resource assignment message having multipletransmit indicators, wherein a position of each transmit indicator inthe message corresponds to a resource unit assigned to a UE, and conveythe resource assignment message using an uplink grant data field on adownlink control message.

The present invention may be more fully described with reference toFIGS. 1-12. FIG. 1 is a block diagram of a wireless communication system100 in accordance with an embodiment of the present invention.Communication system 100 includes multiple user equipment (UEs) 101, 102(two shown) that are each associated with a user, such as but notlimited to a cellular telephone, a radio telephone, a personal digitalassistant (PDA) with radio frequency (RF) capabilities, or a wirelessmodem that provides RF access to digital terminal equipment (DTE) suchas a laptop computer. Communication system 100 further includes awireless communications network 130 that provides communication servicesto each of UEs 101 and 102 via an air interface 120. Network 130includes a Node B 140 in wireless communication with UEs 101 and 102 andfurther includes an edge gateway 150 in communication with the Node B.Each of Node B 104 and edge gateway 150 may be referred to as an elementof wireless network 140. Air interface 120 comprises a downlink 122 andan uplink 124. Each of downlink 122 and uplink 124 comprises multiplephysical communication channels, including multiple reference andcontrol channels, including at least one shared control channel, andmultiple traffic channels.

Node B 140 and edge gateway 150 each includes a respective processor142, 152, such as one or more microprocessors, microcontrollers, digitalsignal processors (DSPs), combinations thereof or such other devicesknown to those having ordinary skill in the art. The particularoperations/functions of processors 142 and 152, and respectively thus ofNode B 140 and edge gateway 150, are determined by an execution ofsoftware instructions and routines that are stored in a respective atleast one memory device 144, 154 associated with the processor, such asrandom access memory (RAM), dynamic random access memory (DRAM), and/orread only memory (ROM) or equivalents thereof, that store data andprograms that may be executed by the corresponding processor. Node B 140further comprises at least one transmitter 146 and at least one receiver148 for transmission and reception of information via air interface 120.

FIG. 2 is a block diagram of a user equipment (UE) 200, such as UEs 101and 102, in accordance with an embodiment of the present invention. UE200 includes a processor 202, such as one or more microprocessors,microcontrollers, digital signal processors (DSPs), combinations thereofor such other devices known to those having ordinary skill in the art.The particular operations/functions of processor 202, and respectivelythus of UE 200, is determined by an execution of software instructionsand routines that are stored in a respective at least one memory device204 associated with the processor, such as random access memory (RAM),dynamic random access memory (DRAM), and/or read only memory (ROM) orequivalents thereof, that store data and programs that may be executedby the corresponding processor. UE 200 further comprises at least onetransmitter 206 and at least one receiver 208 for transmission andreception of information via air interface 120.

Unless otherwise specified herein, the embodiments of the presentinvention preferably are implemented within UEs 101 and 102, Node B 140,and edge gateway 150, and more particularly with or in software programsand instructions stored in the respective at least one memory device204, 144, 154 and executed by the respective processors 202, 142, 152 ofthe UEs, Node B, and edge gateway. However, one of ordinary skill in theart realizes that the embodiments of the present invention alternativelymay be implemented in hardware, for example, integrated circuits (ICs),application specific integrated circuits (ASICs), and the like, such asASICs implemented in one or more of UEs 101 and 102, Node B 140, andedge gateway 150. Based on the present disclosure, one skilled in theart will be readily capable of producing and implementing such softwareand/or hardware without undo experimentation.

Communication system 100 comprises a wideband packet data communicationsystem that employs an Orthogonal Frequency Division Multiplexing (OFDM)modulation scheme for transmitting data over air interface 120.Preferably, communication system 100 is an Orthogonal Frequency DivisionMultiple Access (OFDMA) communication system, wherein a frequencybandwidth is split into multiple frequency sub-carriers that comprisethe physical layer channels over which traffic and signaling channelsare transmitted in a TDM or TDM/FDM fashion. A user may then be assignedone or more of the frequency sub-carriers for an exchange of bearerinformation, thereby permitting multiple users to transmitsimultaneously on the different set of sub-carriers such that eachuser's transmission is orthogonal to the other users' transmissions.Further, communication system 100 preferably operates in accordance withthe 3GPP (Third Generation Partnership Project) E-UTRA (EvolutionaryUMTS Terrestrial Radio Access) standards, which standards specifywireless telecommunications system operating protocols, including radiosystem parameters and call processing procedures. However, those who areof ordinary skill in the art realize that communication system 100 mayoperate in accordance with any wireless telecommunication systememploying an Orthogonal Frequency Division Multiplexing (OFDM)modulation scheme, such as a 3GPP2 (Third Generation Partnership Project2) Evolution communication system, for example, a CDMA (Code DivisionMultiple Access) 2000 1XEV-DV communication system, a Wireless LocalArea Network (WLAN) communication system as described by the IEEE(Institute of Electrical and Electronics Engineers) 802.xx standards,for example, the 802.11a/HiperLAN2, 802.11g, or 802.16 standards, or anyof multiple proposed ultrawideband (UWB) communication systems.

Communication system further provides for guaranteed delivery of datapackets conveyed over air interface 120, for example, by use of any wellknown guaranteed-delivery protocol such as an automatic repeat request(ARQ) protocol or a hybrid ARQ (HARQ) protocol. As is known in the art,such protocols use acknowledgments, such as an ACK and/or a NACK, toidentify data packets that have been correctly received, erroneouslyreceived, or not received.

In order to selectively schedule the multiple UEs 101, 102 for use ofone or more sub-carriers of a frequency bandwidth employed bycommunication system 100, network 130, and in particular Node B 140,provides each UE 101, 102 with an downlink control message, preferablyan uplink scheduling grant, via a control channel of downlink 122. Thegrant includes a UE identifier (UE ID), scheduling information for ascheduling period, an uplink resource assignment, a duration of theassignment, uplink transmission parameters, and an acknowledgment(ACK/NACK) response corresponding to HARQ. The UE ID indicates a UE (ora group of UEs) for which the grant is intended. The uplink transmissionparameters indicate transmission parameters, such as a modulationscheme, a payload size, MIMO-related information, and so on, that theidentified UE (or group of UEs) shall use. The scheduling informationtypically includes a reference start time, preferably in units of radioframes such as a starting Cell System Frame Number (SFN) index or astarting Connection Frame Number (CFN) index, a scheduling duration,that is, a duration of a time period during which the providedscheduling information is applicable, for example, in units of radioframes or Transmission Time Intervals (TTIs), and an allocated uplinkresource unit. In one embodiment of the present invention, the UE may beexpressly informed of an uplink resource unit and/or a downlinkacknowledgment channel to be monitored by the UE. In another embodimentof the present invention, the uplink resource unit and/or the downlinkacknowledgment channel to be monitored by the UE may be implicit basedon information included in the grant, such as the downlinkacknowledgment channel being indicated based on the uplink resource unitassigned to the UE.

For example, FIG. 3 is a block diagram of an uplink grant 300, such as afirst resource assignment message, in accordance with an embodiment ofthe present invention. Uplink resource assignment message 300 isassembled by Node B 140 and conveyed by the Node B to a UE, such as UEs101 and 102, in order to inform the UE of an allocated uplink resourceunit. Uplink grant 300 provides scheduling information (resource unitassignment) for a scheduling period and includes a first data field 302comprising a UE identifier, a second data field 304 comprising uplinkresource unit assignment information, and a third data field 306comprising message length information. The uplink resource unitassignment information identifies an uplink resource unit assigned tothe UE intended as a recipient of the message. As is known in the art,in an OFDMA communication system, a resource unit comprises one or morefrequency sub-carriers in a frequency bandwidth that may assigned to auser for an exchange of user information.

By way of another example, FIG. 4 is a block diagram of an uplink grant400, such as a second resource assignment message, in accordance withanother embodiment of the present invention. Similar to uplink resourceassignment message 300, uplink grant 400 is assembled by Node B 140 andconveyed by the Node B to a UE, such as UEs 101 and 102, in order toinform the UE of an allocated uplink resource unit. Uplink grant 400also provides scheduling information for a scheduling period andincludes a first data field 420 comprising a UE identifier and a seconddata field 430 comprising an uplink resource unit bit map. Uplinkresource unit bit map 430 comprises multiple data fields 401-412 thatare each associated with a 0/1 bit sequence that is used to map eachresource unit (RE) assigned to the UE identified in the message, such asUE 101 or UE 102. That is, each data field 401-412 provides anindication whether a resource unit associated with that data field isassigned to the UE during a next scheduling period, such as aTransmission Time Interval (TTI) or a radio frame transmission period.

Each of UEs 101 and 102 may be a member of a group of UEs 110. FIG. 5 isa table diagram illustrating an exemplary group scheduling setup inaccordance with an embodiment of the present invention. UEs in thissetup are initially classified into three separate groups based on theirpath loss (this information can inferred from downlink C/I or downlinkpilot SNR measurements). That is, UEs with group ID 1301 are in theworst channel conditions for example, have the highest path loss, UEswith group ID 1501 are in the most favorable channel conditions, and UEswith group IDs 1401-1406 are in intermediate channel conditions. Once aUE is assigned a group ID, the UE only needs to ‘wake up’ according to apredetermined pattern specific to that group ID. For instance, a UE withgroup ID 1401 may wake up every 10^(th) subframe while a UE with groupID 1301 may wake up for 3 subframes in every 10 subframes. In each 0.5millisecond (ms) subframe, one (1) long block (LB) is reserved forcontrol signaling and the remaining five (5) LBs are shared amongdifferent UEs for data transmission. As an example, resources within aparticular subframe are shared in a TDM fashion, that is, if two UEsshare a subframe, one UE is allocated two (2) LBs and the other UE isallocated three (3) LBs. A UE scheduled in a particular subframe then isallowed to transmit using only those modulation coding scheme (MCS)levels that are allowed for its group (as shown in Table 3 of FIG. 5).One may note that with this setup, information about which exact MCS touse and which exact resources to transmit in can be conveyed to the UEsscheduled in a particular subframe by using a simple bit map whoselength is equal to the number of UEs that have been assigned aparticular group ID associated with that subframe. One may further notethat, as the UEs transmit their packets, a scheduler can get a betteridea about the channel conditions and uplink interference for each UEusing ACK/NACK information. For instance, if the scheduler notices thata UE with group ID 1401 is dropping packets, it can move that UE togroup 1301 which has more resources reserved for it (thereby allowingmore retransmission opportunities). A grouping of UEs is described infurther detail in U.S. patent application Ser. No. 11/243,033, filedOct. 4, 2005 and entitled “Scheduling in Wireless CommunicationSystems,” which application is assigned to the assignee of the presentinvention and is hereby incorporated herein in its entirety.

Based on the uplink grant, a UE, such as UEs 101 and 102, is able todetermine a downlink acknowledgment (ACK/NACK) channel associated with,and to be monitored by, the UE. A downlink acknowledgment channel iscontained within the shared control channel allocation at the beginningof the sub-frame. Also, distributed allocation is used for theacknowledgment channel. ACK/NACK transmissions are code-multiplexedusing orthogonal sequences. To achieve maximum frequency diversity andavoid strong interference at a particular frequency range, ACK/NACKtransmissions are code-multiplexed using orthogonal sequences or low orzero correlation sequences within a predefined time frequency regionthat is distributed across the entire OFDM symbol. Code DivisionMultiplexing (CDM) allows for easy power assignment/stealing betweenacknowledgments for different users. Different acknowledgments remainorthogonal or minimally correlated in the downlink so there is minimalinterference from other acknowledgments. The number of requiredspreading sequences is dependent on the maximum number of data streamsin the uplink (including MIMO operation). This includes data streamsthat are multiplexed into a resource region assigned to a group. Forinstance, 16 users may be multiplexed into one group with 8 userstransmitting at the same time. Note that only one group is active withina TTI. As an example, for a 5 MHz system, 24 unique acknowledgements maybe supported using a GCL sequence of length 24 that are uniformlydistributed throughout 300 available sub-carriers of an OFDMAcommunication system.

The UE determines the downlink acknowledgment channel based on theresource units assigned to the UE in the uplink grant. For example,suppose a spreading code comprising a CAZAC (Constant Amplitude ZeroAuto-Correlation) sequence is being utilized for uplink transmissions bya UE. Since there are a limited number of time shifts of a CAZACsequence, only a limited number of uplink resource units may be assignedto the UE. For example, in uplink grant 400, the multiple data fields401-412 that are each used to map a resource unit (RE) may eachcorrespond to a time shift of a CAZAC sequence. Thus each data field ofthe twelve data fields 401-412 of resource bit map 430 corresponds toone of twelve time shifts, including a no shift position, of a CAZACsequence in a shifting of the sequence a full cycle. Each time shiftcomprises an assignable uplink channel and each UE 101, 102 knows, thatis, maintains in the UE's at least one memory device 204, the time shiftof the CAZAC sequence corresponding to each 0/1 bit sequence in the bitmap. Network 130, and in particular Node B 140, then informs a UE, suchas one of UEs 101 and 102, that is the intended recipient of themessage, of the uplink resource units been assigned to the UE for agiven time period by including an appropriate value, for example, anappropriate bit, in each bit sequence 401-412 of bit map 430. Thus, eachbit sequence 401-412 may be thought of as a transmit indicator for theUE. In turn, a UE, such as UEs 101 and 102, is able to determine whetherit has been scheduled to transmit via uplink 124, and further determinethe uplink channel assigned to the UE during the time period, based onthe transmit indicators included in the uplink resource assignmentmessage.

For example, as depicted in message 400, “1's” are embedded in datafields 404, 405, 409, and 412, and “0's” are embedded in data fields401-403, 406-408, 410, and 411. A “1” corresponds to an assignment of anuplink resource unit during a next scheduling period and a “0”corresponds to a failure to assign an uplink resource unit during thenext scheduling period for that particular UE. Based on bit map 430, aUE identified in data field 420, such as UE 101, knows to use uplinkresource units 404, 405, 409, and 412 during the next scheduling period.The UE, that is, UE 101, then always looks for a downlink 122acknowledgment (ACK/NACKs) of an uplink 124 transmission of the UE usingan ACK/NACK sequence ID that is based on the UEs first resource unitassignment in the resource assignment message received by the UE. Thatis, with reference to bit map 430, Node B 140 conveys an acknowledgmentto UE 101 on downlink 122, and UE 101 looks for an acknowledgment ondownlink 122, using sequence number 4, which sequence corresponds to thefirst resource unit assignment, that is, resource unit 404, in theuplink grant conveyed by the Node B to the UE. In other words, each UE101, 102 maintains, in the at least one memory device 204 of the UE, alist of spreading codes/sequences, such as Walsh codes or CAZACsequences, and any time shifts associated with such spreadingcodes/sequences, that may be assigned as uplink data channels anddownlink acknowledgment channels and an association between suchspreading codes/sequences/time shifts and the bit sequences in bit map430. Based on a received resource unit assignment message, a UE assigneda resource unit may determine, based on an uplink resource unitassignment, a corresponding downlink acknowledgment (ACK/NACK) channelto monitor for acknowledgments.

By way of another example and further with respect to uplink grant 400,suppose the uplink grant is used to assign uplink resource units tomembers of a group of UEs or to both non-group member UEs and members ofa group of UEs. Further, suppose a first set of data fields 401-408, anda corresponding first set of spreading sequences, are reserved for useby individual users, or UEs, and a second set of data fields 409-412,and a corresponding second set of spreading sequences, are reserved foruse by members of the group. As used herein, different spreadingsequences comprise spreading sequences that may be differentiated basedon values included in the sequence or code or based on different timeshifts applied to a same sequence or code. The non-group users willreceive their uplink resource unit assignments as described in detailabove, except that they will not be assigned, and will not look for,uplink resource units associated with data fields 409-412. On the otherhand, rather than send an uplink grant to each individual member of thegroup, Node B 140 may send an uplink grant, such as uplink grant 400, toall members of the group. Each member of the group then decodes thegrant and determines whether the member has been assigned an uplinkresource unit, and a corresponding downlink acknowledgment channel,based on the member's position in the group. Again, each UE 101, 102maintains, in the at least one memory device 204 of the UE, a list ofspreading codes/sequences and any time shifts associated with suchspreading codes/sequences, that may be assigned as uplink data channelsand downlink acknowledgment channels and an association between suchspreading codes/sequences/time shifts and the bit sequences in bit map430.

That is, suppose that UE 101 is in a first position in the group, forexample, group 110, and UE 102 is in a second position in the group.Further, suppose a spreading code comprising a CAZAC (Constant AmplitudeZero Auto-Correlation) sequence is being utilized by each UE in group110 to transmit on the uplink. The CAZAC sequence is shared by, andknown to, each UE in group 110 for uplink transmissions and there areonly a limited number of possible time shifts of the code before thecode is shifted a full cycle, for example, twelve possible time shifts.Again, each time shift comprises an assignable uplink channel and eachUE that is a member of group 110 knows the time shift corresponding tothat UE. As is known in the art, each UE that is a member of the groupknows its position in the group, that is, a first UE, for example, UE101, knows that it is the first UE in the group, a second UE, forexample, UE 102, knows that it is the second UE in the group, and so on.Based on each UE's position in the group, each UE knows where to look inuplink resource unit bit map 430 for an assignment of an uplink resourceunit to the UE. For example, first UE 101 knows that its correspondingbit in bit map 430 is a first bit sequence in the bit sequences reservedto the group, that is, bit sequence 409, second UE 102 knows that itscorresponding bit in bit map 430 is a second bit sequence in the bitsequences reserved to the group, that is, bit sequence 410, and so on.Node B 140 then informs each UE that is a member of the group whether anuplink resource unit has been assigned to the UE for a given time periodby including an appropriate value, for example, an appropriate bit, inthe data field of bit map 430 corresponding to that UE. Thus, each valueincluded in data fields 401-412 may be thought of as a transmitindicator for the associated UE. In turn, each UE 101-112 is able todetermine whether it has been scheduled to transmit via uplink 124, andfurther determine an uplink channel assigned to the UE and a downlinkacknowledgment channel to be monitored by the UE during the associatedscheduling period, based on the transmit indicator associated with theUE. After informing a UE 101, 102 of the uplink resource unit(s)assigned to the UE and expressly or implicitly a downlink acknowledgmentchannel assigned to the UE, Node B 140 then acknowledges data receivedfrom the UE by code multiplexing acknowledgments intended for the UE byuse of a spreading sequence or code, for example, an orthogonal codesuch as Walsh Code or a Walsh-Hadamard code, or a non-orthogonal but lowor zero correlation code such as a CAZAC sequence, monitored by the UEand which spreading sequence or code is distributed across the frequencybandwidth. Further, each spreading code may be individually powercontrolled by Node B 140 across the frequency bandwidth during thatscheduling period.

Referring now to FIG. 6, an exemplary block diagram 600 is provided thatillustrates a spreading of multiple downlink acknowledgments across anOFDMA frequency bandwidth in accordance with an embodiment of thepresent invention. FIG. 6 includes a time-frequency diagram 640 and apower distribution diagram 650. A vertical scale of time-frequencydiagram 640 depicts multiple blocks 601-612 of frequency sub-carriers ofa frequency bandwidth of communication system 100. A horizontal scale oftime-frequency diagram 640 depicts multiple blocks 621-627 of time of asub-frame that may be allocated. As depicted in time-frequency diagram640, during a first time period corresponding to blocks of time 621 and622, all of the multiple blocks 601-612 of frequency sub-carriers arereserved for reference and shared control signaling. That is, duringblocks of time 621 and 622, all of the channels of communication system100 are control channels. During a second time period corresponding toblocks of time 623-627, all of the multiple blocks 601-612 of frequencysub-carriers are available for a conveyance of data, such as VoIP data,to UEs 101, 102.

Power distribution diagram 650 depicts an allocation of power to eachdownlink acknowledgment channel assigned to a UE, such as UEs 101 and102. As depicted in power distribution diagram 650, a first quantity ofpower 651 is allocated to a first spreading sequence, a second quantityof power 652 is allocated to a second spreading sequence, a thirdquantity of power 653 is allocated to a third spreading sequence, afourth quantity of power 654 is allocated to fourth spreading sequence,and a fifth quantity of power 655 is allocated to a fifth spreadingsequence, for a total power allocation 660 to the downlinkacknowledgment channels during the next scheduling period. (For example,it is assumed here that data field 401 in uplink grant 400 includes a‘1’ rather than a ‘0.’)

Preferably, power is allocated to each downlink acknowledgment channelbased on a channel condition associated with the UE that is, in turn,associated with the downlink acknowledgment channel. For example, Node B140 may determine a channel condition in association with each UE 101,102 serviced by the Node B and active in a coverage area of the Node B.In one embodiment of the present invention, each UE 101, 102 may measurea downlink channel condition, preferably measuring Channel QualityInformation (CQI) as is known in the art, associated with eachsub-carrier of a bandwidth employed by communication system 100 toproduce multiple downlink channel measurements. One of ordinary skill inthe art realizes that many parameters may be measured in determiningchannel quality and that any such parameter may be used herein withoutdeparting from the spirit and scope of the present invention. As isknown in the art, each UE 101, 102 measures channel conditions for eachand every sub-band during a measuring period, such as a TransmissionTime Interval (TTI) (also known as a sub-frame) or a radio frametransmission period. Each UE of the multiple UEs 101, 102 then reportsthe measured channel conditions for all of the sub-bands to servingnetwork 130, and in particular to Node B 140, preferably in a ChannelQuality Information (CQI) message.

In another embodiment of the present invention, Node B 140 may measurean uplink channel condition for each UE 101, 102 serviced by the Node Bbased on uplink transmissions received from the UE, such as an uplinkpilot signal, an uplink control signal, or an uplink traffic signal. Oneof ordinary skill in the art realizes that there are many ways for aNode B to determine channel conditions associated with a UE serviced bythe Node B, and any such method may be used herein without departingfrom the spirit and scope of the present invention.

Based on the channel condition measurements associated with each UE 101,102, Node B 140 may determine a downlink transmit power level for theacknowledgment channel associated with the UE. Node B 140 then transmitsacknowledgements to the UE via downlink 122 of air interface 120 at thedownlink power level determined for the UE until a next downlink powerlevel update period. For example, an OFDMA power allocation scheme isdescribed in detail in U.S. patent application No. 60/759,800, filed onJan. 18, 2006, and entitled “Method and Apparatus for Uplink ResourceAllocation in a Frequency Division Multiple Access CommunicationSystem,” which application is assigned to the assignee of the presentinvention and is hereby incorporated herein in its entirety. Althoughthe power allocation scheme described therein is an uplink powerallocation scheme, one of ordinary skill in the art can apply the powerallocation scheme described therein to allocate downlink transmit powerlevel for the acknowledgment channels allocated by communication system100.

Referring again to FIG. 6, each acknowledgment sequence is then spreadover multiple sub-carriers, that is, over at least one sub-carrier ineach of multiple shared control channel resource blocks. Furthermore,the acknowledgment sequences utilized with respect to each of themultiple UEs allowed to transmit during a scheduling period and,therefore, allocated downlink acknowledgment channels, such as UEs 101and 102, is spread over the same sub-carriers as the acknowledgmentsequences utilized with respect to the other UEs of the multiple UEsallowed to transmit during the scheduling period and allocated downlinkacknowledgment channels. For example, as depicted in FIG. 6, theacknowledgment sequences for each of the multiple UEs transmittingduring the scheduling period, that is UEs 101 and 102, are spread overthe sub-carriers 631-636 during block of time 622.

Referring now to FIGS. 7 and 8, an operation of Node B 140 in conveyingdownlink acknowledgments to one or more UEs, such as one or more of UEs101, 102, is illustrated in accordance with an embodiment of the presentinvention. FIG. 7 is a block diagram of an architecture of Node B 140 inaccordance with an embodiment of the present invention. Node B 140includes multiple sequence spreaders 702 ₁-702 _(N), wherein eachsequence spreader of the multiple sequence spreaders 702 ₁-702 _(N) isassociated with a UE, such as UEs 101, 102, or a group of UEs, such asgroup 110. Each sequence spreader of the multiple sequence spreaders 702₁-702 _(N) is coupled to a respective gain adjuster of multiple gainsadjusters 704 ₁-704 _(N) and, in turn, each of the multiple gainadjusters 704 ₁-704 _(N) is coupled to a combiner 706. Combiner 706 isfurther coupled to an OFDMA mapping function 708 that is, in turncoupled to multiple OFDMA modulators 710 ₁-710 _(P). Each OFDMAmodulator of the multiple OFDMA modulators 710 ₁-710 _(P) is furthercoupled to a respective power amplifier of multiple power amplifiers 712₁-712 _(P), and each power amplifier of the multiple power amplifiers712 ₁-712 _(p) s is further coupled to a respective antenna of multipleantennas 714 ₁-714 _(P). Preferably, each of the multiple sequencespreaders 702 ₁-702 _(N), multiple gain adjusters 704 ₁-704 _(N),combiner 706, OFDMA mapping function 708, and multiple OFDMA modulators710 ₁-710 _(P) is implemented in processor 142 of Node B 140 based onprograms maintained in the at least one memory device 144 of the Node B.Further, preferably each of the multiple power amplifiers 712 ₁-712 _(P)is implemented in the at least one transmitter 146 of the Node B.

FIG. 8 is a logic flow diagram 800 illustrating method executed by NodeB 140 in conveying downlink acknowledgments to one or more UEs inaccordance with an embodiment of the present invention. Logic flowdiagram 800 begins when each sequence spreader 702 ₁-702 _(N) of theNode B receives (802) an acknowledgment, such as one or more bits,intended for the associated UE or group and spreads (804) the receivedacknowledgment based on a respective predetermined spreading sequenceW₁-W_(N) to produce a spread acknowledgment. Each sequence spreader 702₁-702 _(N) then conveys the spread acknowledgment to a respective gainadjuster 704 ₁-704 _(N). Each gain adjuster 704 ₁-704 _(N) adjusts (806)a power of the received spread acknowledgment based on the determineddownlink transmit power level for the acknowledgment channel associatedwith the corresponding UE or group, as described in detail above, toproduce a gain adjusted spread acknowledgment. Each gain adjuster 704₁-704 _(N) then conveys the gain adjusted spread acknowledgment producedby the UE to a combiner 706, which combiner combines (808), for example,sums, the gain adjusted spread acknowledgments received from gainadjusters 704 ₁-704 _(N) to produce combined gain adjusted spreadacknowledgments.

Combiner 706 conveys the combined gain adjusted spread acknowledgmentsto an OFDMA mapping function 708. OFDMA mapping function 708 is coupledto multiple OFDMA modulators 710 ₁-710 _(P). While the operation ofOFDMA mapping function 708, OFDMA modulators 710 ₁-710 _(P), poweramplifiers 712 ₁-712 _(P), and antennas 714 ₁-714 _(P) is describedherein with respect to a forward path through a OFDMA modulator 710 ₁,power amplifier 712 ₁, and antenna 714 ₁, one of ordinary skill in theart realizes that the same signal processing applies to transmission ofthe combined gain adjusted spread acknowledgments through forward pathscomprising any of OFDMA modulators 710 ₂-710 _(P), power amplifiers 712₂-712 _(P), and antennas 714 ₂-714 _(P).

OFDMA mapping function 708 comprises a Serial-to-Parallel (S/P)converter. In response to receiving the combined gain adjusted spreadacknowledgments from combiner 706, OFDMA mapping function 708distributes (810) the combined acknowledgments across the frequencybandwidth. In other words, the combined gain adjusted spreadacknowledgments are applied to multiple sub-carriers across thefrequency bandwidth, rather than applying the acknowledgments to asingle frequency sub-carrier or individually applying eachacknowledgment to a separate, single frequency sub-carrier. In oneembodiment of the present invention, OFDMA mapping function 708 appliesa portion of the combined gain adjusted spread acknowledgments, that is,a portion of each gain adjusted spread acknowledgment of the combinedgain adjusted spread acknowledgments, to each sub-carrier of multipleorthogonal sub-carriers, in effect converting a symbol stream from aserial to a parallel form and producing ‘M’ parallel acknowledgmentstreams, wherein M is the number of sub-carriers allocated forconveyance of the acknowledgments and each parallel stream comprises adifferent portion of the combined gain adjusted spread acknowledgment,that is, a portion of each gain adjusted spread acknowledgment of thecombined gain adjusted spread acknowledgments. OFDMA mapping function708 then applies the M parallel streams to OFDMA modulator 710 ₁. Inanother embodiment of the present invention, OFDMA mapping function 708may replicate the combined gain adjusted spread acknowledgments. OFDMAmapping function 708 then applies a replicated combined gain adjustedspread acknowledgment to each sub-carrier of multiple orthogonalsub-carriers, producing ‘M’ parallel acknowledgment streams, wherein Mis the number of sub-carriers allocated for conveyance of theacknowledgments. OFDMA mapping function 708 then applies the M parallelstreams to OFDMA modulator 710 ₁.

Referring now to FIG. 9, in one embodiment of the present invention,OFDMA mapping function 708 may distribute the combined acknowledgmentsthroughout the frequency bandwidth. Referring now to FIG. 10, in anotherembodiment of the present invention, OFDMA mapping function 708 maydistribute the combined acknowledgments in a localized portion of thefrequency bandwidth. An advantage of a localized distribution of theacknowledgments is that the interference generated by transmission ofthe combined acknowledgments over air interface 120 may then be bettercoordinated.

OFDMA modulator 710 ₁ transforms (812) each acknowledgment of the Mparallel acknowledgments, each of which acknowledgments is assigned to afrequency sub-band, that is, a frequency domain sub-carrier, to a timedomain signal, that is, a time domain sub-carrier, thereby producingmultiple (M) modulated orthogonal time domain sub-carriers, wherein eachsub-carrier corresponds to a sub-carrier included in the frequencybandwidth. The multiple orthogonal frequency sub-bands f_(n)(t), n=0, 1,. . . , M-1 can be thought of as sinusoids or complex exponentials ofthe form e^(j2Π(W/M)int) for t ε [0, T_(total)] where W is the availablefrequency bandwidth and W/M expresses the frequency spacing betweensubcarriers.

As known in OFDM systems, the functionality of OFDMA modulator 710 ₁ maybe implemented with an inverse fast Fourier transform (IFFT), oralternatively with an inverse discrete Fourier transform (IDFT). The Mparallel symbols are provided as input to the IFFT and the IFFT outputsM parallel time domain sub-carriers of frequency f_(n), wherein eachsub-carrier of the M parallel sub-carriers is modulated by acorresponding input acknowledgment of the M parallel input symbols.OFDMA modulator 710 ₁ then converts the modulated time domainsub-carriers constituting the IFFT output to a serial form to produce abaseband output signal that the OFDMA modulator 710 ₁ upconverts from abaseband frequency to a transmit frequency (f_(c)) to produce anupconverted output signal. The upconverted signal is conveyed to poweramplifier 712 ₁. Power amplifier 712 ₁ amplifies the signal to producean amplified signal and transmits (814) the amplified signal to the UEsbeing provided acknowledgments, that is, UEs 101, 102, via antenna 714 ₁and downlink 122 of air interface 120. Logic flow 800 then ends.However, in another embodiment of the present invention, Node B 140 mayfurther apply a different cyclic shift to the signal applied to eachantenna 714 ₁-714 _(P), thereby providing cyclic shift transmitdiversity and further reducing the interference of the transmitteddownlink signals with each other and providing improved reception at theUEs. Cyclic shift transmit diversity is well-known in the art and willnot be described in greater detail herein.

OFDMA modulators, such as OFDMA modulators 710 ₁-710 _(P), arewell-known in the art. For example, FIG. 11 is a block diagram of anexemplary OFDMA modulator 1100, such as OFDMA modulators 710 ₁-710 _(P),in accordance with an embodiment of the present invention. OFDMAmodulator 1100 comprises a transformer 1102, such as an IFFT, coupled toa cyclic prefix (CP) adder 1104. CP adder A04 is coupled to a symbolshaper 1106, the symbol shaper is further coupled to an I/Q modulator1108, and the I/Q modulator is further coupled to an upconverter 1110.As described above, OFDMA modulator 1100 receives multiple parallelstreams of acknowledgments from OFDMA mapping function 708, wherein eachparallel stream comprises acknowledgments for all UEs being conveyed anacknowledgment, such as UEs 101 and 102. OFDMA modulator 1100 routes themultiple parallel acknowledgment streams to transformer 1102, whichtransforms each acknowledgment streams of the multiple parallelacknowledgment streams, each of which acknowledgment streams is assignedto a frequency sub-carrier, that is, a frequency domain sub-carrier, toa time domain signal, that is, a time domain sub-carrier, therebyproducing multiple (M) modulated orthogonal time domain sub-carriers.Transformer 1102 then routes each time domain sub-carriers of themodulated orthogonal time domain sub-carriers to CP adder 1104. CP adderappends a guard band interval, or cyclic prefix, to each received signaland conveys the appended signals to symbol shaper 1106. Symbol shaper1106 shapes each signal received from CP adder 1104 in accordance withwell-known techniques and conveys the shaped signal to I/Q modulator1108. I/Q modulator 1108 then produces an in-band (I) signal and aquadrature (Q) signal for each signal received from symbol shaper 1106and converts the signals from a parallel form to a serial form that theI/Q modulator 1108 then routes to upconverter 1110. Upconverter 1110upconverts the signal received from I/Q Modulator 1108 from a basebandfrequency to a transmit frequency (f_(c)) to produce an upconvertedoutput signal that then is conveyed to a power amplifier, such as poweramplifiers 712 ₁-712 _(P),.

FIG. 12 is a logic flow diagram 1200 illustrating a reception of anacknowledgment by a UE, such as UEs 101 and 102, that has been scheduledfor a downlink acknowledgment channel during a given time period inaccordance with an embodiment of the present invention. Logic flow 1200begins when the UE monitors (1202) a downlink control channel andreceives (1204), via the downlink control channel, an uplink grantinforming the UE of one or more allocated uplink resource units. Asdescribed in detail above, the uplink grant provides schedulinginformation (resource unit assignment) for a scheduling period andincludes a UE identifier and uplink resource unit assignmentinformation, such as one or more identified uplink resource units or oneor more transmit indicators. Based on the one or more identified uplinkresource units or one or more transmit indicators, the UE determines(1206) a downlink acknowledgment channel to monitor, which downlinkacknowledgment channel comprises a selected spreading sequence or codecorresponding to a selected acknowledgment sequence number. Further,based on the received uplink grant, the UE determines (1208) that it isscheduled to transmit data during a given time period based on theuplink grant and transmits (1210) data via one or more of the identifieduplink resource units during the time period.

In response to transmitting the data, the UE monitors (1212) thedetermined downlink acknowledgment channel and receives (1214) anacknowledgment corresponding to the UE's uplink transmission viamultiple sub-carriers, wherein the acknowledgment comprises thespreading sequence or code associated with the UE and determined by theUE based on the one or more identified uplink resource units or one ormore transmit indicators and wherein the spreading sequence or code isdistributed over the multiple sub-carriers in the frequency bandwidth.The UE then decodes (1216) the acknowledgment using the selectedspreading sequence or code, and logic flow diagram 1200 then ends.

By spreading each acknowledgment of multiple acknowledgments with aselected spreading sequence of multiple spreading sequences to producemultiple spread acknowledgments, wherein each acknowledgment is intendedfor a different UE of multiple UEs, and distributing the multiple spreadacknowledgments across the multiple frequency sub-carriers of whentransmitting the acknowledgments to user equipment via a downlink, andfurther individually power controlling each acknowledgment multiplespread acknowledgments, communication system 110 provides for downlinkresource allocation and acknowledgments to multiple users and furtherguarantees accurate detection and decoding at an edge of a cell withoutconsuming an inordinate amount of system power and bandwidth. As usedherein, different spreading sequences comprise spreading sequences thatmay be differentiated based on values included in the sequence or codeor based on different time shifts applied to a same sequence or code.The UE may be expressly notified of a downlink acknowledgement channelcomprising the spreading sequence to be monitored by the UE, or the UEimplicitly may determine a downlink acknowledgment channel based on anuplink resource unit allocation in an uplink grant that is conveyed tothe UE via a downlink control channel. Further, the grant may explicitlyidentify the uplink resource unit(s) allocated to the UE or mayimplicitly identify the uplink resource unit(s) allocated to the UEbased on a transmit indicator included in the grant. In addition, whenthe UE is allocated multiple uplink resource units, the downlinkacknowledgment channel to be monitored by the UE may comprise a downlinkacknowledgment channel associated with a first resource unit of themultiple resource units allocated to the UE. Furthermore, when the UE isa member of a group, the UE may determine the uplink resource unit(s)allocated to the UE, and correspondingly the downlink acknowledgmentchannel to be monitored by the UE, based on an uplink grant conveyed tothe members of the group and a position of the UE in the group.

While the present invention has been particularly shown and describedwith reference to particular embodiments thereof, it will be understoodby those skilled in the art that various changes may be made andequivalents substituted for elements thereof without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather then a restrictive sense, and all such changes and substitutionsare intended to be included within the scope of the present invention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any variation thereof, are intended tocover a non-exclusive inclusion, such that a process, method, article,or apparatus that comprises a list of elements does not include onlythose elements but may include other elements not expressly listed orinherent to such process, method, article, or apparatus. Furthermore,unless otherwise indicated herein, the use of relational terms, if any,such as first and second, top and bottom, and the like are used solelyto distinguish one entity or action from another entity or actionwithout necessarily requiring or implying any actual such relationshipor order between such entities or actions.

1. A method for providing downlink acknowledgments corresponding touplink transmission using hybrid automatic repeat request to a pluralityof users in an Orthogonal Frequency Division Multiplexing communicationsystem wherein a frequency bandwidth comprises a plurality of frequencysub-carriers, the method comprising: spreading each acknowledgment of aplurality of acknowledgments with a selected spreading sequence of aplurality of spreading sequences to produce a plurality of spreadacknowledgments; using a first resource unit assigned to a userequipment in an uplink scheduling grant and for an uplink transmissionto select a downlink acknowledgment channel number for the userequipment; and distributing the plurality of spread acknowledgmentsacross the plurality of frequency sub-carriers.
 2. The method of claim1, wherein the plurality of spreading sequences are associated uniquelywith a plurality of users.
 3. The method of claim 1, further comprisingchoosing a transmission power of the spread acknowledgement sequence fora user based on a received Channel Quality Information of the user. 4.The method of claim 1, wherein each spreading sequence of the pluralityof spreading sequences is orthogonal to the other spreading sequences ofthe plurality of spreading sequences.
 5. The method of claim 1, whereineach spreading sequence of the plurality of spreading sequencescomprises a CAZAC sequence.
 6. The method of claim 1, wherein a firstset of spreading sequences are used for individual user equipment and asecond set of spreading sequences are used by members of a group of userequipment.
 7. A wireless network element that provides downlinkacknowledgments corresponding to uplink transmission using hybridautomatic repeat request to a plurality of users in an OrthogonalFrequency Division Multiplexing communication system wherein a frequencybandwidth comprises a plurality of frequency sub-carriers, wherein thewireless network element comprises: a processor that is configured touse a first resource unit assigned to a user equipment in an uplinkscheduling grant and for an uplink transmission to select a downlinkacknowledgment channel number for the user equipment, spread eachacknowledgment of a plurality of acknowledgments with a selectedspreading sequence of a plurality of spreading sequences to produce aplurality of spread acknowledgments, and distribute the plurality ofspread acknowledgments across the plurality of frequency sub-carriers.8. The wireless network element of claim 7, wherein the plurality ofspreading sequences are associated uniquely with a plurality of users.9. The wireless network element of claim 7, wherein the processor isfurther configured to choose a transmission power of the spreadacknowledgement sequence for a user based on a received Channel QualityInformation of the user.
 10. The wireless network element of claim 7,wherein each spreading sequence of the plurality of spreading sequencesis orthogonal to the other spreading sequences of the plurality ofspreading sequences.
 11. The wireless network element of claim 7,wherein each spreading sequence of the plurality of spreading sequencescomprises a CAZAC sequence.
 12. The wireless network element of claim 7,wherein a first set of spreading sequences are used for individual userequipment and a second set of spreading sequences are used by members ofa group of user equipment.
 13. A user equipment (UE) that receives anacknowledgment corresponding to uplink hybrid automatic repeat requesttransmission in an Orthogonal Frequency Division Multiplexingcommunication system wherein a frequency bandwidth comprises a pluralityof frequency sub-carriers, the user equipment comprising: a processorthat is configured to monitor a downlink control channel informing theUE of an uplink grant, determine that the UE is scheduled to transmitdata during a given time period based on the uplink grant, transmit dataduring the time period, receive an acknowledgment corresponding to theUE's uplink transmission via a plurality of sub-carriers, wherein theacknowledgment comprises a spreading sequence associated with the UE andwherein the spreading sequence is distributed over the plurality ofsub-carriers in the frequency bandwidth, and decode the acknowledgmentusing a selected acknowledgment sequence number, wherein the processoris configured to determine the acknowledgment spreading sequence numberbased on a first resource unit assigned to the user equipment in theuplink grant and wherein the resource unit is assigned to the userequipment for an uplink transmission.
 14. The user equipment of claim13, wherein the spreading sequence is orthogonal to spreading sequencesused to convey acknowledgments to other user equipment via the samemultiple sub-carriers.
 15. The user equipment of claim 13, wherein thespreading sequence comprises a CAZAC sequence with a time shift that isdifferent than time shifts applied to acknowledgments conveyed to otheruser equipment via the same multiple sub-carriers.
 16. The userequipment of claim 13, wherein the spreading sequence used depends uponwhether or not the user equipment is a member of a group.
 17. The userequipment of claim 13, wherein the selected acknowledgment sequencenumber is based on the resource unit of the plurality of resource unitsassigned to the user equipment.